How to make it smell nice

I think heavily scented flowers are the best option but not the cheapest.

What about those little air fresheners that aren't aerosols? Do you know the ones I mean, they stand upright and have scented gel inside. I put them in the ladies' loos at my wedding. They aren't pretty to look at but you could hide them.

Flowers!! unless anything is particuly dusty/moulding then it wont smell. ive sat in church at other peoples weddings and with guests mixed perfumes/hairsprays/lotions/aftershaves the place didn't have room for any more smells! but if your really worried asda do really cheap car freshners for 50p each in various fruit smells/vanilla etc and they are really strong and could be hidden or tied under tables or chairs.

Arran aromatics do room sprays to match their scented candles and they smell really nice, not too over powering and not "chemically" if that makes sense.

How about fragrence sticks like these?

What about fragranced hearts -

You could have them in your colour scheme.

I'd go with flowers.

I hate obviously chemically fragranced things like plug ins, scented stick, scented bog roll etc. They make me feel sick and seem so heavy.

If you aren't having enough flowers to scent the room, how about dried lavender in the centrepieces or in scented hearts like above.

Are you a summer wedding? If so the walls of the marquee may well be open with a constant breeze which will most probably counteract any air freshening or flower scents in place!